THE PRESENT INVENTION relates to a safety arrangement in a motor vehicle.
It has been proposed to provide safety arrangements in a motor vehicle which incorporate an air-bag adapted to be inflated in the event that an accident should occur to provide protection for the driver or an occupant of a vehicle. It has been customary to mount an air-bag intended to provide protection for a front seat passenger of a motor vehicle in the event that a frontal impact should occur within the dashboard of the motor vehicle. The air-bag is associated with an appropriate sensor arrangement which initiates inflation of the air-bag in the event that a frontal impact should occur.
When the air-bag is inflated, the fabric of the air-bag may be given, at least initially, a very substantial velocity directed towards the occupant of the front seat. If the occupant of the front seat is not in an appropriate position, that is to say, is not sitting fully back in the seat, then difficulties may arise. If, for example, the occupant of the seat is leaning forwardly at the instant that the air-bag is inflated, the air-bag may impact severely with the occupant of the seat and may impart substantial injuries to the occupant of the seat.
If the occupant of the front seat is very heavy, then the occupant of the seat will require much more xe2x80x9ccushioningxe2x80x9d in the event that a frontal impact should arise than a very light occupant of the seat. Thus, it is desirable to be able to inflate an air-bag which has been provided to protect the occupant of a front seat in the event of a frontal impact, in dependence upon the weight of the occupant of the seat.
It has been proposed before to control the inflation of an air-bag provided to protect a front seat passenger in a motor vehicle. DE OS 2516185 discloses an arrangement in which a switch is provided within the squab of the seat. If the occupant is sitting on the seat, the switch is closed, and in the event that an accident should occur, the air-bag is fully inflated. However, if the switch is not closed, which is a situation which might obtain if the occupant of the seat is not actually sitting on the seat, but instead is standing in front of the seat, then the air-bag is only partially inflated.
DE 3809074 also discloses an arrangement in which sensors are located between the squab of the seat and the floor of the motor vehicle to determine the downward forces applied at the front and at the rear of the seat, to determine the position of the occupant of the seat and thus to control the inflation characteristic of an air-bag.
Sensors that have been utilised previously have been designed to resist the forces which may be applied to the sensors in an accident situation. These forces can be extremely high. It has proved to be extremely difficult to provide a sensor which has sufficient strength, but which can provide a reliable and accurate determination of the forces applied to the seat during ordinary driving conditions. Many of the sensors that have been used before are such that the measurement of the force is determined as a consequence of a movement of one part of the sensor relative to another part of the sensor. Any frictional effects between the two parts of the sensor causes the sensor to provide an incorrect reading and also, if the occupant of a seat changes position there may be a substantial time delay (at least relative to the time available to inflate an air-bag during an accident situation, which is usually measured as a few tens of milliseconds) before a correct output signal is provided.
The present invention seeks to provide an improved safety arrangement.
According to this invention there is provided a safety arrangement in a motor vehicle, the safety arrangement comprising a seat to be occupied by a passenger of the vehicle, a plurality of sensors located between the seat and the floor of the vehicle, each adapted to provide an indication of the downward force applied to it, control means adapted to initiate and control the inflation of an air-bag and adapted to receive signals from the sensors, and adapted to control the inflation of the air-bag in dependence upon the nature of the said signals, the sensors comprising means which, at least in ordinary use of the seat, form the sole connection between the seat and the floor of the motor vehicle, each sensor comprising a first portion connected directly or indirectly to the floor of the motor vehicle, and a second portion connected directly or indirectly to the seat, said two portions being inter-connected by a deformable element having sensor means responsive to deformation thereof.
Preferably the first portion of each sensor is mounted on a carriage slideable along a rail mounted on the floor of a motor vehicle and the second portion of each sensor is connected to a sub-frame of the seat.
Conveniently the element inter-connecting the first and second portions of each sensor comprises a cantilever beam adapted to deflect when a downward force is applied to the portion connected to the seat.
In one embodiment the cantilever element has one end connected to a mounting block comprising said first portion, the mounting block having means securing the mounting block to part of the carriage, and has the other end connected to a mounting block, that other mounting block having means securing the mounting block to part of a sub-frame for the seat.
In an alternative embodiment each sensor comprises an integral element, the element having a first portion mounted to a carriage slidably mountable in a rail connected to the floor of the vehicle and a second portion connected to the sub-frame of a seat, the two portions being inter-connected by a cantilever element.
Preferably part of the carriage is located adjacent part of the sub-frame, one of said parts carrying a projection of a predetermined diameter, said projection being located within an aperture of slightly greater diameter formed in the other part, the arrangement being such that in the event that a substantial force is applied to the seat, the projection carried by the one part will engage the wall of the aperture carried by the other part.
Conveniently the said one part comprises a web carried by the carriage, and the other part comprises a flange carried by a support element forming part of the sub-frame, the carriage carrying a bolt having a threaded portion passing through a bore provided in the web and having a portion of enlarged diameter, defining a shoulder with the threaded portion, the portion of enlarged diameter extending through said aperture which is formed in a flange provided on a support element forming pail of the sub-frame of the seat.